Technique to reduce the zeolite molecular sieve solubility in an aqueous system

ABSTRACT

An improvement to an adsorbent comprising a crystalline aluminosilicate used in a process for separating a component from a feed mixture comprising an aqueous solution of a mixture of different components, such as a mixture of saccharides. There is an undesirable tendency for the silicon constituent of the crystalline aluminosilicate to dissolve in the aqueous system. The adsorbent has incorporated in it a binder material comprising a water permeable organic polymer which substantially reduces the undesirable dissolution. The adsorbent is manufactured by mixing together powder of the crystalline aluminosilicate, powders of the organic polymer binder, and a liquid organic solvent, forming the mixture into discrete formations, preferably by extruding the mixture into an extrudate, and drying the formations. The improvement comprises spheronizing those formations prior to drying them.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The field of art to which this invention pertains is solid-bedadsorptive separation. More specifically, the invention relates to animprovement to an adsorbent, and an improved process for separating acomponent from a mixture comprising an aqueous solution of a mixture ofdifferent components which process employs an adsorbent comprising acrystalline aluminosilicate which selectively adsorbs a component fromthe feed mixture.

2. Prior Art

It is known in the separation art that certain crystallinealuminosilicates referred to as zeolites can be used in the separationof a component from an aqueous solution of a mixture of differentcomponents. For example, adsorbents comprising crystallinealuminosilicate are used in the method described in U.S. Pat. No.4,014,711 to separate fructose from a mixture of sugars in aqueoussolution including fructose and glucose.

It is also known that crystalline aluminosilicates or zeolites are usedin adsorption processing in the form of agglomerates having highphysical strength and attrition resistance. Methods for forming thecrystalline powders into such agglomerates include the addition of aninorganic binder, generally a clay comprising silicon dioxide andaluminum oxide to the high purity zeolite powder in wet mixture. Theblended clay zeolite mixture is extruded into cylindrical type pelletsor formed into beads which are subsequently calcined in order to convertthe clay to an amorphous binder of considerable mechanical strength. Asbinders, clays of the kaolin type are generally used.

Zeolite crystal and inorganic binder agglomerates have long been knownto have the property of gradually disintegrating as a result ofcontinuous contact with water. This disintegration has been observed asa silicon presence or contamination in the solution in contact with theadsorbent. Such contamination may at times be sufficiently severe toimpart a cloudy appearance to the solution.

It has been discovered that the disintegration of the adsorbent may beminimized by substituting a water permeable organic polymer for theinorganic binder material. The adsorbent is made by mixing together apowder of the zeolite crystal, a powder of the polymer and a liquidorganic solvent to form a malleable mixture. The mixture is then formedinto discrete formations and dried.

We have discovered an improvement to an adsorbent having a waterpermeable organic polymer binder which enables even further reduction ofits extent of disintegration in aqueous service.

SUMMARY OF THE INVENTION

Accordingly, the objectives of our invention are (1) to develop animproved adsorbent composition suitable for use in a process for theseparation of a component from a feed mixture comprising differentcomponents in aqueous solution by contacting the mixture with animproved adsorbent comprising a crystalline aluminosilicate so as tominimize the dissolution of the crystalline aluminosilicate and silicacontamination of the product.

In brief summary, our invention is, in one embodiment, an adsorbentcomprising a crystalline aluminosilicate suitable for use in a processfor the separation of a component from a feed mixture comprising anaqueous solution of a mixture of components by contacting the solutionwith the adsorbent. The silicon constituent of the adsorbent tends todissolve in the solution resulting in the undesirable disintegration ofthe crystalline aluminosilicate. The adsorbent is bound by a bindermaterial comprising a water permeable organic polymer whichincorporation substantially reduces the extent of dissolution of thesilicon constituent and the extent of the disintegration of theadsorbent. The method of manufacture of the adsorbent comprises: (a)mixing together a powder of crystalline aluminosilicate, a powder of thebinder and a liquid organic solvent to form a malleable mixture; (b)forming the malleable mixture into discrete formations; (c) removing thesolvent from the formations to obtain hard dry formations; and (d)breaking the hard dry formations into particles of desired sizes. Theimprovement to the process comprises spheronizing the formations of step(b) prior to proceeding to step (c), thereby achieving further reductionof the extent of dissolution of the silicon constitutent and the extentof the disintegration of the adsorbent.

In another embodiment, our invention is an adsorbent for use in aprocess for the separation of a compound from a feed mixture comprisingan aqueous solution of a mixture of components by contacting thesolution with the adsorbent of the first mentioned embodiment.

Other objects and embodiments of our invention encompass details aboutfeed mixtures, adsorbents, binder materials, solvents, desorbentmaterials and operating conditions, all of which are hereinafterdisclosed in the following discussions of each of the facets of thepresent invention.

DESCRIPTION OF THE INVENTION

At the outset the definitions of various terms used throughout thesepecification will be useful in making clear the operation, objects andadvantages of the process.

A feed mixture is a mixture containing one or more extract componentsand one or more raffinate components to be separated by our process. Theterm "feed stream" indicates a stream of a feed mixture which passes tothe adsorbent used in the process.

An "extract component" is a component that is more selectively adsorbedby the adsorbent while a "raffinate component" is a component that isless selectively adsorbed. The term "desorbent material" shall meangenerally a material capable of desorbing an extract component. The term"desorbent stream" or "desorbent input stream" indicates the streamthrough which desorbent material passes to the desorbent. The term"raffinate stream" or "raffinate output stream" means a stream throughwhich a raffinate component is removed from the absorbent. Thecomposition of the raffinate stream can vary from essentially 100%desorbent material to essentially 100% raffinate components. The term"extract stream" or "extract output stream" shall mean a stream throughwhich an extract material which has been desorbed by a desorbentmaterial is removed from the adsorbent. The composition of the extractstream, likewise, can vary from essentially 100% desorbent material toessentially 100% extract components. At least a portion of the extractstream, and preferably at least a portion of the raffinate stream, fromthe separation process are passed to separation means, typicallyfractionators or evaporators, where at least a portion of desorbentmaterial is separated to produce an extract product and a raffinateproduct. The terms "extract product" and "raffinate product" meanproducts produced by the process containing, respectively, an extractcomponent and a raffinate component in higher concentrations than thosefound in the extract stream and the raffinate stream.

The term "selective pore volume" of the adsorbent is defined as thevolume of the adsorbent which selectively adsorbs an extract componentfrom the feed mixture. The term "non-selective void volume" of theadsorbent is the volume of the adsorbent which does not selectivelyretain an extract component from the feed mixture. This volume includesthe cavities of the absorbent which contain no adsorptive sites and theinterstitial void spaces between adsorbent particles. The selective porevolume and the non-selective void volume are generally expressed involumetric quantities and are of importance in determining the properflow rates of fluid required to be passed into an operational zone forefficient operations to take place for a given quantity of adsorbent.When adsorbent "passes" into an operational zone (hereinafter definedand described) employed in one embodiment of this process, itsnon-selective void volume, together with its selective pore volume,carries fluid into that zone. The non-selective void volume is utilizedin determining the amount of fluid which should pass into the same zonein a counter-current direction to the absorbent to displace the fluidpresent in the non-selective void volume. If the fluid flow rate passinginto a zone is smaller than the non-selective void volume rate ofadsorbent material passing into that zone, there is a net entrainment ofliquid into the zone by the adsorbent. Since this net entrainment is afluid present in non-selective void volume of the adsorbent, it, in mostinstances, comprises less selectively retained feed components. Theselective pore volume of an adsorbent can in certain instances adsorbportions of raffinate material from the fluid surrounding the adsorbent,since in certain instances there is competition between extract materialand raffinate material for adsorptive sites within the selective porevolume. If a large quantity of raffinate material with respect toextract material surrounds the adsorbent, raffinate material can becompetitive enough to be adsorbed by the adsorbent.

The so-called "simple sugars" are classified as monosaccharides and arethose sugars which upon hydrolysis do not break down into smallersimpler sugars. One may further classify monosaccharides as aldoses orketoses, depending upon whether they are hydroxy aldehydes or hydroxyketones, and by the number of carbon atoms in the molecule. Most commonand well known are probably the hexoses. Common ketohexoses are fructose(levulose) and sorbose; common aldohexoses are glucose (dextrose),mannose and galactose. The term "oligosaccharides", as commonlyunderstood in the art and as used herein, means simple polysaccharidescontaining a known number of constituent monosaccharide units. Anoligosaccharide that breaks up upon hydrolysis into two monosaccharideunits is called a disaccharide, examples being sucrose, maltose, andlactose. Those giving three such units are trisaccharides, of whichraffinose and melezitose are examples. Di-, tri- and tetrasaccharidescomprise practically all of the oligosaccharides. The term"polysaccharide" includes oligosaccharides but usually it refers tocarbohydrate materials of such high molecular weight, namely, those thatare capable of breaking up on hydrolysis into a large number ofmonosaccharide units. Typical polysaccharides are starch, glycogen,cellulose and pentosans.

Feed mixtures which can be charged to the process of the invention may,for example, be aqueous solutions of one or more aldoses and one or moreketoses, or one or more monosaccharides and one or moreoligosaccharides. The concentration of solids in the solutions may rangefrom about 0.5 wt. % to about 50 wt. % or more, but preferably will befrom about 5 to about 35 wt. %. Starch syrups such as corn syrup areexamples of feed mixtures which can be charged to the process. Suchsyrups are produced by the partial hydrolysis of starch generally in thepresence of mineral acids or enzymes. Corn syrup produced in this mannerwill typically contain 25 to 75 wt. % solids comprising 90 to 95%glucose and 5 to 10% maltose and higher oligosaccharides. A portion ofthe glucose in this corn syrup may be isomerized with an isomerizingenzyme to produce a high-fructose corn syrup, typically comprising40-45% fructose, 50-55 % glucose and 5-10% oligosaccharides, which canalso be charged to the process. The pH of the aqueous solutioncomprising the feed mixture may be from about 5.0 to about 8.0.

Desorbent materials used in various prior art adsorptive separationprocesses vary depending upon such factors as the type of operationemployed. In the swing-bed system, in which the selectively adsorbedfeed component is removed from the adsorbent by a purge stream,desorbent selection is not as critical and desorbent material comprisinggaseous hydrocarbons such as methane, ethane, etc., or other types ofgases such as nitrogen or hydrogen, may be used at elevated temperaturesor reduced pressures or both to effectively purge the adsorbed feedcomponent from the adsorbent. However, in adsorptive separationprocesses which are generally operated continuously at substantiallyconstant pressures and temperatures to insure liquid phase, thedesorbent material must be judiciously selected to satisfy manycriteria. First, the desorbent material should displace an extractcomponent from the adsorbent with reasonable mass flow rates withoutitself being so strongly adsorbed as to unduly prevent an extractcomponent from displacing the desorbent material in a followingadsorption cycle. Expressed in terms of the selectivity (hereinafterdiscussed in more detail), it is preferred that the adsorbent be moreselective for all of the extent components with respect to a raffinatecomponent than it is for the desorbent material with respect to araffinate component. Secondly, desorbent materials must be compatiblewith the particular adsorbent and the particular feed mixture. Morespecifically, they must not reduce or destroy the critical selectivityof the adsorbent for an extract component with respect to a raffinatecomponent. Additionally, desorbent materials should not chemically reactwith or cause a chemical reaction of either an extract component or araffinate component. Both the extract stream and the raffinate streamare typically removed from the adsorbent in admixture with desorbentmaterial and any chemical reaction involving a desorbent material and anextract component or a raffinate component would reduce the purity ofthe extract product or the raffinate product or both. Since both theraffinate stream and the extract stream typically contain desorbentmaterials, desorbent materials should additionally be substances whichare easily separable from the feed mixture that is passed into theprocess. Without a method of separating at least a portion of thedesorbent material present in the extract stream and the raffinatestream, the concentration of an extract component in the extract productand the concentration of a raffinate component in the raffinate productwould not be very high, nor would the desorbent material be availablefor reuse in the process. It is contemplated that at least a portion ofthe desorbent material will be separated from the extract and theraffinate streams by distillation or evaporation, but other separationmethod such as reverse osmosis may also be employed alone or incombination with distillation or evaporation. Since the raffinate andextract products are foodstuffs intended for human consumption,desorbent materials should also be non-toxic. Finally, desorbentmaterials should also be materials which are readily available andtherefore reasonable in cost.

Water having a pH of from about 5.0 to about 8.0 satisfies thesecriteria and is a suitable and preferred desorbent material for theprocess. The pH of the desorbent material is important becauseadsorption of a component by the adsorption, removal of a raffinatestream, desorption of the component from the adsorbent and removal of anextract stream all typically occur in the presence of desorbentmaterial. If the desorbent material is too acidic or too alkaline,chemical reactions of the components are promoted and reaction productsare produced that can reduce the yield purity of either the extract orraffinate product, or both.

Water pH does of course vary widely depending upon the source of thewater in addition to other factors. Methods of maintaining andcontrolling a desired water pH are, however, well known to those skilledin the art of water treating. Such methods generally comprise adding analkaline compound such as sodium hydroxide or an acid compound such ashydrochloric acid to the water in amounts as necessary to achieve andmaintain the desired pH.

The prior art has recognized that certain characteristics of adsorbentsare highly desirable, if not absolutely necessary, to the successfuloperation of a selective adsorption process. Such characteristics aregenerally important to this process. Among such characteristics are:adsorptive capacity for some volume of an extract component per volumeof adsorbent; the selective adsorption of an extract component withrespect to a raffinate component and the desorbent material; andsufficiently fast rates of adsorption and desorption of an extractcomponent to and from the adsorbent. Capacity of the adsorbent foradsorbing a specific volume of an extract component is, of course, anecessity; without such capacity the absorbent is useless for adsorptiveseparation. Furthermore, the higher the adsorbent's capacity for anextract component the better is the adsorbent. Increased capacity of aparticular adsorbent makes it possible to reduce the amount of adsorbentneeded to separate an extract component of known concentration containedin a particular charge rate of feed mixture. A reduction in the amountof adsorbent required for a specific adsorptive separation reduces thecost of the separation process. It is important that the good initialcapacity of the adsorbent be maintained during actual use in theseparation process over some economically desirable life. The secondnecessary adsorbent characteristic is the ability of the adsorbent toseparate components of the feed; or, in other words, that the absorbentposses adsorptive selectivity (B), for one component as compared toanother component. Relative selectivity can be expressed not only forone feed component as compared to another but can also be expressedbetween any feed mixture component and the desorbent material. Theselectivity, (B) as used throughout this specification is defined as theratio of the two components of the adsorbed phase over the ratio of thesame two components in the unadsorbed phase at equilibrium conditions.Relative selectivity is shown as Equation 1 below: ##EQU1## where C andD are two components of the feed represented in volume percent and thesubscripts A and U represent the adsorbed and unadsorbed phasesrespectively. The equilibrium conditions were determined when the feedpassing over a bed of adsorbent did not change composition aftercontacting the bed of adsorbent. In other words, there was no nettransfer of material occurring between the unadsorbed and adsorbedphases. Where selectivity of two components approaches 1.0 there is nopreferential adsorption of one component by the adsorbent with respectto the other; they are both adsorbed (or non-adsorbed) to about the samedegree with respect to each other. As the (B) becomes less than orgreater than 1.0 there is a preferential adsorption by the adsorbent forone component with respect to the other. When comparing the selectivityby the adsorbent of one component C over component D, a (B) larger than1.0 indicates preferential adsorption of component C within theadsorbent. A (B) less than 1.0 would indicate that component D ispreferentially adsorbed leaving an unadsorbed phase richer in componentC and an adsorbed phase richer in component D. Ideally, desorbentmaterials should have a selectivity equal to about 1 or slightly lessthan 1 with respect to all extract components so that all of the extractcomponents can be desorbed as a class with reasonable flow rates ofdesorbent material and so that extract components can displace desorbentmaterial in a subsequent adsorption step. While separation of an extractcomponent from a raffinate component is theoretically possible when theselectivity of the adsorbent for the extract component with respect tothe raffinate component is greater than 1.0, it is preferred that suchselectivity be greater than 1.0. Like relative volatility, the higherthe selectivity the easier the separation is to perform. Higherselectivities permit a smaller amount of adsorbent to be used. The thirdimportant characteristic is the rate of exchange of the extractcomponent of the feed mixture material or, in other words, the relativerate of desorption of the extract component. This characteristic relatesdirectly to the amount of desorbent material that must be employed inthe process to recover the extract component from the adsorbent; fasterrates of exchange reduce the amount of desorbent material needed toremove the extract component and therefore permit a reduction in theoperating cost of the process. With faster rates of exchange, lessdesorbent material has to be pumped through the process and separatedfrom the extract stream for reuse in the process.

Adsorbents to be used in the process of this invention will comprisespecific crystalline aluminosilicates or molecular sieves. Particularcrystalline aluminosilicates encompassed by the present inventioninclude crystalline aluminosilicate cage structures in which the aluminaand silica tetrahedra are intimately connected in an open threedimensional network to form cage-like structures with window-like poresof about 8 A free diameter. The tetrahedra are cross-linked by thesharing of oxygen atoms with spaces between the tetrahedra occupied bywater molecules prior to partial or total dehydration of this zeolite.The dehydration of the zeolite results in crystals interlaced with cellshaving molecular dimensions and thus the crystalline aluminosilicatesare often referred to as "molecular sieves", particularly when theseparation which they effect is dependent essentially upon differencesbetween the sizes of the feed molecules as, for instance, when smallernormal paraffin molecules are separated from larger isoparafin moleculesby using a particular molecular sieve.

In hydrated form, the crystalline aluminosilicates used in the processof this invention generally encompass those zeolites represented by theFormula 1 below:

    M.sub.2/n O:Al.sub.2 O.sub.3 :wSiO.sub.2 :yH.sub.2 O       Formula 1

where "M" is a cation which balances the electrovalence of thealuminum-centered tetrahedra and which is generally referred to as anexchangeable cationic site, "n" represents the valence of the cation,"w" represents the moles of SiO₂, and "y" represents the moles of water.The generalized cation "M" may be monovalent, divalent or trivalent ormixtures thereof.

The prior art has generally recognized that adsorbents comprising X andY zeolites can be used in certain adsorptive separation processes. Thesezeolites are described and defined in U.S. Pat. Nos. 2,882,244 and3,120,007 respectively incorporated herein by reference thereto. The Xzeolite in the hydrated or partially hydrated form can be represented interms of mole oxides as shown in Formula 2 below:

    (0.9±0.2)M.sub.2/n O:Al.sub.2 O.sub.3 :(2.50±0.5)SiO.sub.2 :yH.sub.2 O                                                         Formula 2

where "M" represents at least one cation having a valence of not morethan 3, "n" represents the valence of "M", and "y" is a value up toabout 9 depending upon the identity of "M" and the degree of hydrationof the crystal. As noted from Formula 2, the SiO₂ /Al₂ O₃ mole ratio ofX zeolite is 2.5±0.5. The cation "M" may be one or more of a number ofcations such as a hydrogen cation, an alkali metal cation, or analkaline earth cation, or other selected cations, and is generallyreferred to as an exchangeable cationic site. As the X zeolite isinitially prepared, the cation "M" is usually predominately sodium, thatis, the major cation at the exchangeable cationic sites is sodium andthe zeolite is therefore referred to as a sodium-X zeolite. Dependingupon the purity of the reactants used to make the zeolite, other cationsmentioned above may be present, however, as impurities. The Y zeolite inthe hydrated or partially hydrated form can be similarly represented interms of mole oxides as in Formula 3 below:

    (0.9±0.2)M.sub.2/n O:Al.sub.2 O.sub.3 :wSiO.sub.2 :yH.sub.2 O Formula 3

where "M" is at least one cation having a valence not more than 3, "n"represents the valence of "M", "w" is a value greater than about 3 up toabout 6, and "y" is a value up to about 9 depending upon the identity of"M" and the degree of hydration of the crystal. The SiO₂ /Al₂ O₃ moleratio for Y zeolites can thus be from about 3 to about 6. Like the Xzeolite, the cation "M" may be one or more of a variety of cations but,as the Y zeolite is initially prepared, the cation "M" is also usuallypredominately sodium. A Y zeolite containing predominately sodiumcations at the exchangeable cationic sites is therefore referred to as asodium-Y zeolite.

Cations occupying exchangeable cationic sites in the zeolite may bereplaced with other cations by ion exchange methods well known to thosehaving ordinary skill in the field of crystalline aluminosilicates. Suchmethods are generally performed by contacting the zeolite or anadsorbent material containing the zeolite with an aqueous solution ofthe soluble salt of the cation or cations desired to be placed upon thezeolite. After the desired degree of exchange takes place, the sievesare removed from the aqueous solution, washed, and dried to a desiredwater content. By such methods the sodium cations and any non-sodiumcations which might be occupying exchangeable sites as impurities in asodium-X or sodium-Y zeolite can be partially or essentially completelyreplaced with other cations. It is preferred that the zeolite used inthe process of this invention contain cations at exchangeable cationicsites selected from the group consisting of the alkali metals and thealkaline earth metals.

Typically, adsorbents known to the prior are used in separativeprocesses contain zeolite crystals and amorphous material. The zeolitewill typically be present in the adsorbent in amounts ranging from about75 wt. % to about 98 wt. % based on volatile free composition. Volatilefree compositions are generally determined after the adsorbent has beencalcined at 900° C. in order to drive off all volatile matter. Theremainder of the adsorbent will generally be an amorphous inorganicmaterial such as silica, or silica-alumina mixtures or compounds, suchas clays, which material is present in intimate mixture with the smallparticles of the zeolite material. This amorphous material may be anadjunct of the manufacturing process of zeolite (for example,intentionally incomplete purification of either zeolite during itsmanufacture) or it may be added to relatively pure zeolite, but ineither case its usual purpose is as a binder to aid in forming oragglomerating the hard crystalline particles of the zeolite. Normally,the adsorbent will be in the form of particles such as extrudates,aggregates, tablets, macrospheres or granules having a desired particlesize range. The typical adsorbent will have a particle size range ofabout 16-50 mesh (Standard U.S. Mesh). Examples of zeolites used inadsorbents known to the art, either as is or after cation exchange, are"Molecular Sieves 13X" and "SK-40" both of which are available from theLinde Company, Tonawanda, N.Y. The first material of course contains Xzeolite while the latter material contains Y zeolite. It is known that Xor Y zeolites possess the selectivity requirement and other necessaryrequirements previously discussed and are therefore suitable for use inseparation processes.

The adsorbent of our invention has incorporated therein a bindermaterial comprising a water permeable organic polymer. To be waterpermeable, the organic polymer, when a dry solid, will have throughoutits mass small void spaces and channels which will allow an aqueoussolution to penetrate the polymer and thereby come into contact with thezeolite particles bound by the polymer. Cellulose nitrate and/orcellulose esters such as cellulose acetate have been found to beparticularly suitable for use in the adsorbent of our invention. Thepreferred concentration of the organic polymer in the adsorbent is fromabout 3.0 to about 50.0 wt. %.

The adsorbent of our invention is in the form of particles having aparticle size range of about 16-80 mesh (Standard U.S. Mesh). Adsorbentshaving an organic polymer binder do not require calcining, and, mostimportant, achieve substantially reduced disintegration and siliconcontamination of the product stream when used in an aqueous system. Thereduced disintegration results in minimization of the undesirableincrease in pressure drop through the column in which the adsorbent ispacked as compared to the inevitable high increase associated with theadsorbents of the known art.

The adsorbent with an organic polymer binder is manufactured by mixingtogether powder of the crystalline aluminosilicate, powder of theorganic polymer binder, and a liquid organic solvent to make the mixturemalleable, forming the mixture into discrete formations, removing thesolvent from the formations and breaking the formations into the desiredsized particles. The forming of the malleable mixture is preferably doneby extrusion. The aluminosilicate and binder powders may first be mixedtogether and the solvent added to the powder mixture, or the binderpowder may be first dissolved in the solvent and the aluminosilicatepowder added to the solution. Preferred liquid organic solvents arep-dioxane, methylethyl ketone, acetone, chloroform, benzyl alcohol,ethyl acetate and cyclohexanone, any of which may be mixed withformamide. The solvent is removed from the formations either by waterwashing followed by drying at a temperature not exceeding about 100° C.,or by just drying at that temperature. The formations are broken intoparticles having a preferred size such that the particles will passthrough a No. 16 screen and be retained on a No. 80 screen. Any finesresulting from the breaking of the particles not retained on a No. 80screen may be added to the aluminosilicate-solvent-binder mixture. Theparticles may be further treated to effect ion exchange between cationsat exchangeable cationic sites on the crystalline aluminosilicate in theparticles and cations preferably selected from the group consisting ofalkali metals and alkali earth metals.

The improvement to the organic polymer bound adsorbent comprising ourinvention is effected by the spheronization of the malleable discreteadsorbent formations obtained in the course of the adsorbent manufactureprior to removing the solvent from the formations. Spheronization isaccomplished by feeding the adsorbent formations, preferably extrudates,into a special machine which imparts a rolling motion to the formationsthrough action of a horizontal spinning plate in a stationary cylinder.In the first stages of spheronization, the formations are broken intopieces and as rolling progresses, the pieces are shaped into sphericalparticles. The time required to accomplish this shaping may vary fromless than 30 seconds to several minutes depending on the degree ofmalleability of the material.

The particular machine heretofore used by us for spheronization is knownby the trade name "Marumerizer" and is sold by Elanco Products Company,a division of Eli Lilly and Company. Material is fed onto the spinningplate of the Marumerizer and after the spheres are formed, they aredischarged through an opening in the side of the stationary cylinder.The plate is belt-driven through a variable speed drive which can be setto select plate speeds of approximately 400 to 1,600 RPM.

The Marumerizer has long been used in the pharmaceutical industry formaking spherical pelleted products having the advantages of attractiveappearance, free flowing characteristics and the ability to be easilymixed when combination products are desired. We have found thatspheronization as achieved by the Marumerizer and as claimed in ourinvention enables further reductions of silica loss of the organicpolymer bound adsorbents used in aqueous service. We have observed thatspheronization yields a denser adsorbent, which would enable the loadingof adsorbent chambers in less time and the design of smaller chambers,and have also observed that spheronization in fact produces a betterperforming adsorbent from the standpoint of increased retention volumeand decreased tendency to disintegrate. Without being limited to anyparticular theory, we believe the spheronization action forces theorganic polymer into the macropore structure of the zeolite and tobranch out and form a three dimensional matrix, thus accounting for theincreased strength.

The adsorbent may be employed in the form of a dense compact fixed bedwhich is alternatively contacted with the feed mixture and desorbentmaterials. In the simplest embodiment of the invention, the adsorbent isemployed in the form of a single static bed in which case the process isonly semi-continuous. In another embodiment, a set of two or more staticbeds may be employed in fixed-bed contacting with appropriate valving sothat the feed mixture is passed through one or more adsorbent beds whilethe desorbent materials can be passed through one or more of the otherbeds in the set. The flow of feed mixture and desorbent materials may beeither up or down through the desorbent. Any of the conventionalapparatus employed in static bed fluid-solid contacting may be used.

Counter-current moving-bed or simulated moving-bed counter-current flowsystems, however, have a much greater separation efficiency than fixedadsorbent bed systems and are therefore preferred for use in theseparation process. In the moving-bed or simulated moving-bed processesthe adsorption and desorption operations are continuously taking placewhich allows both continuous production of an extract and a raffinatestream and the continual use of feed and desorbent streams. Onepreferred embodiment of this process utilizes what is known in the artas the simulated moving-bed counter-current flow system. The operatingprinciples and sequence of such a flow system are described in U.S. Pat.No. 2,985,589 incorporated herein by reference thereto. In such asystem, it is the progressive movement of multiple liquid access pointsdown an adsorbent chamber that simulates the upward movement ofadsorbent contained in the chamber. Only four of the access lines areactive at any one time; the feed input stream, desorbent inlet stream,raffinate outlet stream, and extract outlet stream access lines.Coincident with this simulated upward movement of the solid adsorbent isthe movement of the liquid occupying the void volume of the packed bedof adsorbent. So that counter-current contact is maintained, a liquidflow down the adsorbent chamber may be provided by a pump. As an activeliquid access point moves through a cycle, that is, from the top of thechamber to the bottom, the chamber circulation pump moves throughdifferent zones which require different flow rates. A programmed flowcontroller may be provided to set and regulate these flow rates.

The active liquid access points effectively divided the adsorbentchamber into separate zones, each of which has a different function. Inthis embodiment of my process, it is generally necessary that threeseparate operational zones be present in order for the process to takeplace although in some instances an optional fourth zone may be used.

The adsorption zone, zone 1, is defined as the adsorbent located betweenthe feed inlet stream and the raffinate outlet stream. In this zone, thefeed stock contacts the adsorbent, an extract component is adsorbed, anda raffinate stream is withdrawn. Since the general flow through zone 1is from the feed stream which passes into the zone to the raffinatestream which passes out of the zone, the flow in this zone is consideredto be a downstream direction when proceeding from the feed inlet to theraffinate outlet streams.

Immediately upstream with respect to fluid flow in zone 1 is thepurification zone, zone 2. The purification zone is defined as theadsorbent between the extract outlet stream and the feed inlet stream.The basic operations taking place in zone 2 are the displacement fromthe non-selective void volume of the adsorbent of any raffinate materialcarried into zone 2 by the shifting of adsorbent into this zone and thedesorption of any raffinate material adsorbed within the selective porevolume of the adsorbent or adsorbed on the surfaces of the adsorbentparticles. Purification is achieved by passing a portion of extractstream material leaving zone 3 into zone 2 at zone 2's upstreamboundary, the extract outlet stream, to effect the displacement ofraffinate material. The flow of material in zone 2 is in a downstreamdirection from the extract outlet stream to the feed inlet stream.

Immediately upstream of zone 2 with respect to the fluid flowing in zone2 is the desorption zone or zone 3. The desorption zone is defined asthe adsorbent between the desorbent inlet and the extract outlet stream.The function of the desorption zone is to allow a desorbent materialwhich passes into this zone to displace the extract component which wasadsorbed upon the adsorbent during a previous contact with feed in zone1 in a prior cycle of operation. The flow of fluid in zone 3 isessentially in the same direction as that of zones 1 and 2.

In some instances, an optional buffer zone, zone 4, may be utilized.This zone, defined as the adsorbent between the raffinate outlet streamand the desorbent inlet stream, if used, is located immediately upstreamwith respect to the fluid flow to zone 3. Zone 4 would be utilized toconserve the amount of desorbent utilized in the desorption step since aportion of the raffinate stream which is removed from zone 1 can bepassed into zone 4 to displace desorbent material present in that zoneout of that zone into the desorption zone. Zone 4 will contain enoughadsorbent so that raffinate material present in the raffinate streampassing out of that zone into the desorption zone. Zone 4 will containenough adsorbent so that raffinate material present in the raffinatestream passing out of zone 1 and into zone 4 can be prevented frompassing into zone 3, thereby contaminating extract stream removed fromzone 3. In the instances in which the fourth operational zone is notutilized, the raffinate stream passed from zone 1 to zone 4 must becarefully monitored in order that the flow directly from zone 1 to zone3 can be stopped when there is an appreciable quantity of raffinatematerial present in the raffinate stream passing from zone 1 into zone 3so that the extract outlet stream is not contaminated.

A cyclic advancement of the input and output streams through the fixedbed of adsorbent can be accomplished by utilizing a manifold system inwhich the valves in the manifold are operated in a sequential manner toeffect the shifting of the input and output streams, thereby allowing aflow of fluid with respect to solid adsorbent in a counter-currentmanner. Another mode of operation which can effect the counter-currentflow of solid adsorbent with respect to fluid involves the use of arotating disc valve in which the input and output streams are connectedto the valve and the lines through which feed input, extract output,desorbent input and raffinate output streams pass are advanced in thesame direction through the adsorbent bed. Both the manifold arrangementand disc valve are known in the art. Specifically, rotary disc valveswhich can be utilized in this operation can be found in U.S. Pat. Nos.3,040,777 and 3,422,848. Both of the aforementioned patents disclose arotary type connection valve in which the suitable advancement of thevarious input and output streams from fixed sources can be achievedwithout difficulty.

In many instances, one operational zone will contain a much largerquantity of adsorbent than some other operational zone. For instance, insome operations the buffer zone can contain a minor amount of adsorbentas compared to the adsorbent required for the adsorption andpurification zones. It can also be seen that in instances in whichdesorbent is used which can easily desorb extract material from theadsorbent that a relatively small amount of adsorbent will be needed ina desorption zone as compared to the adsorbent needed in the buffer zoneor adsorption zone or purification zone or all of them. Since it is notrequired that the adsorbent be located in a single column, the use ofmultiple chambers or a series of columns is within the scope of theinvention.

It is not necessary that all of the input or output streams besimultaneously used, and in fact, in many instances some of the streamscan be shut off while others effect an input or output of material. Theapparatus which can be utilized to effect the process of this inventioncan also contain a series of individual beds connected by connectingconduits upon which are placed input or output taps to which the variousinput or outlet streams can be attached and alternatively andperiodically shifted to effect continuous operation. In some instances,the connecting conduits can be connected to transfer taps which duringthe normal operations do not function as a conduit through whichmaterial passes into or out of the process.

It is contemplated that at least a portion of the extract output streamwill pass into a separation means wherein at least a portion of thedesorbent material can be separated to produce an extract productcontaining a reduced concentration of desorbent material. Preferably,but not necessary to the operation of the process, at least a portion ofthe raffinate output stream will also be passed to a separation meanswherein at least a portion of the desorbent material can be separated toproduce a desorbent stream which can be reused in the process and araffinate product containing a reduced concentration of desorbentmaterial. The separation means will typically be a fractionation columnor an evaporator, the design and operation of either being well known tothe separation art.

Reference can be made to D. B. Broughton U.S. Pat. No. 2,985,589, and toa paper entitled "Continuous Adsorptive Processing--A New SeparationTechnique" by D. B. Broughton presented at the 34th Annual Meeting ofthe Society of Chemical Engineers at Tokyo, Japan, on Apr. 2, 1969, forfurther explanation of the simulated moving-bed counter-current processflow scheme.

A dynamic testing apparatus is employed to test various adsorbents witha particular feed mixture and desorbent material to measure theadsorbent characteristics of adsorptive capacity, selectivity andexchange rate. The apparatus consists of an adsorbent chamber ofapproximately 70 cc volume having inlet and outlet portions at oppositeends of the chamber. The chamber is contained within a temperaturecontrol means and, in addition, pressure control equipment is used tooperate the chamber at a constant predetermined pressure. Quantitativeand qualitative analytical equipment such as refractometers,polarimeters and chromatographs can be attached to the outlet line ofthe chamber and used to detect quantitatively or determine qualitativelyone or more components in the effluent stream leaving the adsorbentchamber. A pulse test, performed using this apparatus and the followinggeneral procedure, is used to determine selectivities and other data forvarious adsorbent systems. The adsorbent is filled to equilibrium with aparticular desorbent material by passing the desorbent material throughthe adsorbent chamber. At a convenient time, a pulse of feed containingknown concentrations of a tracer and of a particular ketose or aldose orboth all diluted in desorbent is injected for a duration of severalminutes. Desorbent flow is resumed, and the tracer and the ketose andaldose are eluted as in a liquid-solid chromatographic operation. Theeffluent can be analyzed on-stream or alternatively effluent samples canbe collected periodically and later analyzed separately by analyticalequipment and traces of the envelopes of corresponding component peaksdeveloped.

From information derived from the test adsorbent, performance can berated in terms of void volume, retention volume for an extract or araffinate component, selectivity for one component with respect to theother, the rate of desorption of an extract component by the desorbentand the extent of silica contamination of the extract and raffinatestream. The retention volume of an extract or a raffinate component maybe characterized by the distance between the center of the peak envelopeof an extract or a raffinate component and the peak envelope of thetracer component or some other known reference point. It is expressed interms of the volume in cubic centimeters of desorbent pumped during thistime interval represented by the distance between the peak envelope.Selectivity, (B), for an extract component with respect to a raffinatecomponent may be characterized by the ratio of the distance between thecenter of the extract component peak envelope and the tracer peakenvelope (or other reference point) to the corresponding distancebetween the center of the raffinate component peak envelope and thetracer peak envelope. The rate of exchange of an extract component withthe desorbent can generally be characterized by the width of the peakenvelopes at half intensity. The narrower the peak width the faster thedesorption rate.

To further evaluate promising adsorbent systems and to translate thistype of data into a practical separation process requires actual testingof the best system in a continuous counter-current moving-bed orsimulated moving-bed liquid-solid contacting device. The generaloperating principles of such a device are as described hereinabove. Aspecific laboratory-size apparatus utilizing these principles isdescribed in deRosset et al U.S. Pat. No. 3,706,812. The equipmentcomprises multiple adsorbent beds with a number of access lines attachedto distributors within the beds and terminating at a rotary distributingvalve. At a given valve position, feed and desorbent are beingintroduced through two of the lines and the raffinate and extractstreams are being withdrawn through two more. All remaining access linesare inactive and when the position of the distributing valve is advancedby one index all active positions will be advanced by one bed. Thissimulates a condition in which the adsorbent physically moves in adirection countercurrent to the liquid flow. Additional details on theabove-mentioned adsorbent testing apparatus and adsorbent evaluation maybe found in the paper "Separation of C₈ Aromatics by Adsorption" by A.J. deRosset, R. W. Neuzil, D. J. Korous, and D. H. Rosback presented atthe American Chemical Society, Los Angeles, Calif., Mar. 28 through Apr.2, 1971.

Although both liquid and vapor phase operations can be used in manyadsorptive separation processes, liquid-phase operation is required forthis process because of the lower temperature requirements and becauseof the higher yields of extract product that can be obtained withliquid-phase operation over those obtained with vapor-phase operation.Adsorption conditions will include a temperature range of from about 20°C. to about 200° C. with about 20° C. to about 100° C. being morepreferred and a pressure range of from about atmospheric to about 500psig. with from about atmospheric to about 250 psig. being morepreferred to insure liquid-phase. Desorption conditions will include thesame range of temperatures and pressures as used for adsorptionconditions.

The size of the units which can utilize the process of this inventioncan vary anywhere from those of pilot-plant scale (see for example ourassignee's U.S. Pat. No. 3,706,812) to those of commercial scale and canrange in flow rates from as little as a few cc an hour up to manythousands of gallons per hour.

The following examples are presented to illustrate the invention and arenot intended to unduly restrict the scope and spirit of the claimsattached hereto.

EXAMPLE I

The purpose of this example is to illustrate the method of manufactureof the adsorbent of our invention.

10.5 lbs. of commercial Y zeolite (23.8% volatile matter as measured byloss on ignition at 900° C.) was weighed out and blended with 2 lbs. ofcellulose acetate (39.8% acetyl content). This blend was then admixedwith 2500 cc of a 65% glacial acetic acid solution. The resulting dough,after intensive mixing, was extruded through a 0.03" die.

Four 500 cc portions of the extrudate were obtained and each was placedin a Marumerizer and marumerized to a different degree, i.e. twoportions for 4 minutes, one at a setting of 475 revolutions per minuteand the other at a setting of 550 revolutions per minute, and the othertwo portions for 7 minutes, one at a setting of 475 revolutions perminute and the other at a setting of 550 revolutions per minute. Eachportion of marumerized extrudate was then dried in a dry system oven for6 hours at 200° F. followed by 2 hours at 250° F. The material was thencrushed and sized between 30-50 mesh screens.

Following are the densities measured for each portion as well as thedensity of a control sample prepared exactly as above except for themarumerization (spheronization) step.

    ______________________________________                                                             Piece Density                                            ______________________________________                                        Unmarumerized adsorbent (control)                                                                    1.152                                                  Marumerized @ 4 minutes                                                       Setting 475 rev/minute 1.185                                                  Setting 550 rev/minute 1.224                                                  Marumerized @ 7 minutes                                                       Setting 475 rev/minute 1.167                                                  Setting 550 rev/minute 1.232                                                  ______________________________________                                    

It is apparent from the above that spheronization yields higher densityadsorbent.

EXAMPLE II

The purpose of this example is to present the results of tests of thatadsorbent in the above Example I spheronized for 7 minutes at a settingof 550 revolutions per minute, as well as comparative data for claybound and un-spheronized organic polymer bound adsorbents. Each examplewas calcium ion exchanged in an upflow reactor by contacting theadsorbent with a calcium chloride solution at a 2 liquid hourly spacevelocity for 12 hours. The tests were conducted in the dynamic testingapparatus hereinbefore described to determine the performance of eachsuch adsorbent with regard to the adsorptive separation of theindividual components of an aqueous solution of a mixture of components.

The adsorbents were tested in a 70 cc coiled column maintained at aprocess of 55° C. and 50 psig pressure using pure water having a pH of7.0 as the desorbent material. The sequence of operations for each testwere as follows. Desorbent material was continuously run through thecolumn containing the adsorbent at a nominal liquid hourly spacevelocity (LHSV) of about 1.0. At a convenient time desorbent flow wasstopped, a 4.7 cc sample of 10 wt. % fructose in water was injected intothe column via a sample loop and the desorbent flow was resumed. Theemergent sugar was detected by means of a continuous refractometerdetector and a peak envelope trace was developed. Another pulsecontaining 10 wt. % glucose was similarly run as was a pulse ofdeuterium oxide. Deuterium oxide has a different index of refractionthan does water and thus deuterium oxide can be detected with therefractometer in the same way as is done for the sugars. The use of afeed pulse containing deuterium oxide therefore permits calculation ofadsorbent selectivity for an extract component (fructose) with respectto water. A water sucrose solution was also injected to serve as atracer from which the void volume of the adsorbent bed could bedetermined. Thus for each adsorbent tested for peak traces weredeveloped, one for fructose, one for glucose, one for deuterium oxideand one for sucrose. The retention volume for glucose was calculated bymeasuring the distance from time zero or the reference point to themidpoint of the glucose peak and subtracting the distance representingthe void volume of the adsorbent obtained by measuring the distance fromthe same reference point to the midpoint of the sucrose peak. In asimilar manner retention volumes for fructose and deuterium oxide wereobtained.

The selectivities of an adsorbent for fructose with respect to glucoseand for fructose with respect to water are the quotients obtained bydividing the fructose retention volume by the glucose retention volumeand by dividing the fructose retention by the deuterium oxide retentionvolume respectively. The results for these pulse tests are as follows:

    ______________________________________                                                              Mixed    Marumerized Mixed                              Adsorbent   Clay Based                                                                              Matrix   Matrix                                         ______________________________________                                        Halfwidth                                                                     Fructose    14.0      13.79    16.1                                           Glucose     12.0      12.26    12.6                                           Sucrose     12.6      12.81    12.7                                           D.sub.2 O   10.0      11.8     11.9                                           Retention Volume                                                              Fructose    13.2      10.41    11.6                                           Glucose     2.4       1.96     2.5                                            D.sub.2 O   12.6      12.21    15.7                                           Selectivity                                                                   B (F/G)     5.5       5.32     4.70                                           B (F/D.sub.2 O)                                                                           1.0       0.85     0.74                                           ______________________________________                                    

By spheronization, the retention volumes of the mixed matrix (organicpolymer bound) adsorbent are increased and become substantially similarto the retention volumes of the clay based adsorbent. At the same timeit was observed that the spheronized adsorbent exhibited improvementover the un-spheronized mixed matrix adsorbent with regard to resistanceto dissolution. Spheronization is thus clearly beneficial and an advancein the art of adsorbent manufacture.

We claim as our invention:
 1. A method for the preparation of acrystalline aluminosilicate adsorbent which comprises the steps of:(a)mixing together a powdered crystalline aluminosilicate, a powderedbinder comprising a water permeable organic polymer and a liquid organicsolvent to form a malleable mixture; (b) forming said malleable mixtureinto discrete formations; (c) then spheronizing said formations; and (d)thereafter removing said solvent from the resultant spheres to producehard, dry spherical particles.
 2. The method of claim 1 furthercharacterized in that the forming of said malleable mixture in step (b)is effected by extrusion.
 3. The method of claim 1 further characterizedin that said hard dry formations of step (d) are broken into particlesof desired sizes.
 4. The method of claim 1 further characterized in thatsaid water permeable organic polymer comprises a cellulose ester orcellulose nitrate.
 5. The method of claim 1 further characterized inthat said crystalline aluminosilicate is selected from the groupconsisting of X zeolites and Y zeolites.
 6. The method of claim 5further characterized in that said aluminosilicate contains cations atexchangeable cationic sites selected from the group consisting of alkalimetals and alkali earth metals.
 7. Speroidal adsorbent particlesprepared by the method of claim 1.